package com.fan.sgginterview;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * @author :  PF_23
 * @Description : 读写锁:手写一个缓存
 * 多个线程同时读一个资源类没有问题，所以为了满足并发量，读取共享资源应该可以同时进行。但是写共享
 * 资源只能有一个线程。
 * 写操作：原子+独占，整个过程必须是一个完整的统一体，中间不许被分割，被打断。
 * @date : 2020/04/10.
 */
// 资源类
class MyCache {
    private volatile Map<String, Object> map = new HashMap<>();

    // private Lock lock = new ReentrantLock();
    private ReentrantReadWriteLock reentrantReadWriteLock = new ReentrantReadWriteLock();

    public void put(String key, Object value) {
        reentrantReadWriteLock.writeLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + "\t 正在写入：" + key);
            try {
                TimeUnit.MILLISECONDS.sleep(300);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            map.put(key, value);
            System.out.println(Thread.currentThread().getName() + "\t 写入完成");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            reentrantReadWriteLock.writeLock().unlock();
        }
    }

    public void get(String key) {
        reentrantReadWriteLock.readLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + "\t 正在读取：");
            try {
                TimeUnit.MILLISECONDS.sleep(300);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            Object result = map.get(key);
            System.out.println(Thread.currentThread().getName() + "\t 读取完成" + result);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            reentrantReadWriteLock.readLock().unlock();
        }
    }
}

public class ReadWriteLockDemo {

    public static void main(String[] args) {
        MyCache myCache = new MyCache();
        for (int i = 1; i <= 5; i++) {
            final int tempInt = i;
            new Thread(() -> {
                myCache.put(tempInt + "", tempInt + "");
            }, String.valueOf(i)).start();
        }

        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println();
        System.out.println();
        System.out.println();
        System.out.println();

        for (int i = 1; i <= 5; i++) {
            final int tempInt = i;
            new Thread(() -> {
                myCache.get(tempInt + "");
            }, String.valueOf(i)).start();
        }
    }
}

